1. Field
The disclosed concept pertains generally to vacuum interrupters for protecting electric power circuits and, more particularly, to vacuum interrupters or vacuum envelopes including a movable electrode. The disclosed concept also pertains to retainers for the movable electrode of a vacuum interrupter. The disclosed concept further pertains to electrical switching apparatus, such as vacuum circuit interrupters, including a number of vacuum interrupters.
2. Background Information
Vacuum interrupters include separable main contacts disposed within an insulated and hermetically sealed vacuum chamber. The vacuum chamber typically includes a number of sections of ceramics (e.g., a number of tubular ceramic portions) for electrical insulation capped by a number of end members (e.g., without limitation, metal components, such as metal end plates; end caps; seal cups) to form an envelope in which a vacuum may be drawn. The ceramic section is typically cylindrical; however, other suitable cross-sectional shapes may be used. Two end members are typically employed. Where there are multiple ceramic sections, an internal center shield is disposed between the ceramic sections.
Vacuum circuit interrupters (e.g., without limitation, vacuum circuit breakers; vacuum switches; load break switches) provide protection for electrical systems from electrical fault conditions such as current overloads, short circuits, and low level voltage conditions. Typically, vacuum circuit interrupters include a spring-powered or other suitable operating mechanism, which opens electrical contacts inside a number of vacuum interrupters to interrupt the current flowing through the conductors in an electrical system in response to abnormal conditions.
The main contacts of vacuum interrupters are electrically connected to an external circuit to be protected by the vacuum circuit interrupter by electrode stems, typically an elongated member made from high purity copper. Generally, one of the contacts is fixed relative to the vacuum chamber as well as to the external circuit. The fixed contact is mounted in the vacuum envelope on a first electrode extending through one end member. The other contact is movable relative to the vacuum envelope. The movable contact is mounted on a movable electrode axially slidable through the other end member. The movable contact is driven by the operating mechanism and the motion of the operating mechanism is transferred inside the vacuum envelope by a coupling that includes a sealed metallic bellows. The fixed and movable contacts form a pair of separable contacts which are opened and closed by movement of the movable electrode in response to the operating mechanism located outside of the vacuum envelope. The electrodes, end members, bellows, ceramic shell(s), and the internal shield, if any, are joined together to form the vacuum interrupter capable of maintaining a vacuum at a suitable level for an extended period of time.
Known technology for a bushing for the movable electrode of a vacuum interrupter employs a plastic bushing in contact with the movable electrode and a metal retainer which holds the bushing in place. For example, the plastic bushing and the metal retainer include mating octagonal features, the plastic bushing and the movable electrode are disposed at and protrude from the bottom (or top) of the vacuum interrupter, and the metal retainer is disposed at the bottom (or top) of the plastic bushing. A portion of the metal retainer is spot welded to one vacuum interrupter end member or seal cup.
Some vacuum interrupters employ mounting studs near the movable electrode at the bottom (or top) of the vacuum interrupter for mounting to a vacuum circuit interrupter structure. The limited space between the movable electrode and the mounting studs prevents the use of the plastic bushing and the metal retainer, since the plastic bushing needs some mating feature in order that the metal retainer can rigidly hold the plastic bushing.
There is room for improvement in vacuum envelopes and vacuum interrupters employing a retainer and a bushing for a movable electrode.
There is also room for improvement in vacuum circuit interrupters, which employ a vacuum interrupter including a retainer and a bushing for a movable electrode.
There is further room for improvement in retainers and bushings for a movable electrode of a vacuum interrupter.